Structures and stability of defect-free multiwalled carbon toroidal rings

Atomistic simulations of the structures and stability of defect-free multiwalled carbon toroidal rings were performed using the second-generation empirical bond-order potential and a Morse-type van der Waals potential. It was found that a multiwalled toroidal ring improves the structural stability over its outermost single-walled counterpart, implying a stabilizing effect from the inner rings. This can be explained by the superlinear relation between the critical ring diameter and its tube diameter existing in single-walled rings. However, the findings that the critical diameter of an armchair ring is larger than that of a zigzag ring with the same tube diameters, and that the inclusion of torsion exhibits a negative effect on the stability of a multiwalled ring, are in contrast to that of a single-walled nanoring. In addition, the instability of a multiwalled nanoring always starts with the formation of many short-wavelength ripples on the compressed side of the outermost tube. Subsequently, some of the ripples develop into buckles, resulting in buckling failures.